diff --git a/pkg/compiler/lib/src/serialization/element_serialization.dart b/pkg/compiler/lib/src/serialization/element_serialization.dart
index 3182596edc2..7069b51ff56 100644
--- a/pkg/compiler/lib/src/serialization/element_serialization.dart
+++ b/pkg/compiler/lib/src/serialization/element_serialization.dart
@@ -8,6 +8,7 @@ import '../common.dart';
 import '../constants/constructors.dart';
 import '../constants/expressions.dart';
 import '../dart_types.dart';
+import '../diagnostics/messages.dart';
 import '../elements/elements.dart';
 import '../elements/modelx.dart' show ErroneousElementX;
 import 'constant_serialization.dart';
@@ -213,8 +214,8 @@ class ErrorSerializer implements ElementSerializer {
     encoder.setEnum(Key.MESSAGE_KIND, element.messageKind);
     if (element.messageArguments.isNotEmpty) {
       MapEncoder mapEncoder = encoder.createMap(Key.ARGUMENTS);
-      element.messageArguments.forEach((String key, String value) {
-        mapEncoder.setString(key, value);
+      element.messageArguments.forEach((String key, var value) {
+        mapEncoder.setString(key, Message.convertToString(value));
       });
     }
   }
diff --git a/pkg/compiler/lib/src/serialization/type_serialization.dart b/pkg/compiler/lib/src/serialization/type_serialization.dart
index 3d4cb9fd353..24a46ae27f8 100644
--- a/pkg/compiler/lib/src/serialization/type_serialization.dart
+++ b/pkg/compiler/lib/src/serialization/type_serialization.dart
@@ -35,7 +35,9 @@ class TypeSerializer extends DartTypeVisitor<dynamic, ObjectEncoder> {
     encoder.setTypes(Key.NAMED_PARAMETER_TYPES, type.namedParameterTypes);
   }
 
-  void visitMalformedType(MalformedType type, ObjectEncoder encoder) {}
+  void visitMalformedType(MalformedType type, ObjectEncoder encoder) {
+    encoder.setElement(Key.ELEMENT, type.element);
+  }
 
   void visitInterfaceType(InterfaceType type, ObjectEncoder encoder) {
     encoder.setElement(Key.ELEMENT, type.element);
@@ -79,8 +81,11 @@ class TypeDeserializer {
         return new TypedefType(decoder.getElement(Key.ELEMENT),
             decoder.getTypes(Key.TYPE_ARGUMENTS, isOptional: true));
       case TypeKind.STATEMENT:
-      case TypeKind.MALFORMED_TYPE:
         throw new UnsupportedError("Unexpected type kind '${typeKind}.");
+      case TypeKind.MALFORMED_TYPE:
+        // TODO(johnniwinther): Do we need the 'userProvidedBadType' or maybe
+        // just a toString of it?
+        return new MalformedType(decoder.getElement(Key.ELEMENT), null);
       case TypeKind.DYNAMIC:
         return const DynamicType();
       case TypeKind.VOID:
diff --git a/tests/compiler/dart2js/serialization/test_data.dart b/tests/compiler/dart2js/serialization/test_data.dart
index 950a211e68a..562b21d7cf1 100644
--- a/tests/compiler/dart2js/serialization/test_data.dart
+++ b/tests/compiler/dart2js/serialization/test_data.dart
@@ -400,6 +400,20 @@ class A {
   noSuchMethod(_) => null;
   m();
 }
+''',
+  }),
+
+  const Test('Malformed types', const {
+    'main.dart': '''
+import 'a.dart';
+
+main() {
+  m();
+}
+''',
+  }, preserializedSourceFiles: const {
+    'a.dart': '''
+Unresolved m() {}
 ''',
   }),
 ];